1. Field of the Invention
The present invention relates generally to two-degree-of-freedom (TDOF) gyroscopes and more particularly to TDOF gyroscopes of the flexible disk type. Specifically, the present invention relates to damping mechanisms for such gyroscopes for damping axial vibrations of the rotor at vibration frequencies resonant with the natural frequency of the rotor.
2. Description of the Prior Art
TDOF gyroscopes utilizing a spinning flexible disk rotor for sensing angular turning rates about orthogonal axes, each orthogonal to each other and to the rotor spin axis are well known in the art as exemplified by U.S. Pat. Nos. 3,323,377 and 3,998,105. As disclosed therein, a thin flexible disk is mounted on the end of a shaft spun at relatively high rotational velocities by a spin motor. Rotation of the gyro housing about the orthogonal axes results in a processional deflection of the flexible disk rotor relative to its plane of rotation proportional to the rate of such rotation. Suitable electrical transducers supported on the gyro housing on the orthogonal axes are provided for providing electrical signals proportional to such precession and hence proportional to the input angular rates.
While the principles of the flex disk gyro have been known for many years, these have been limited, if any, practical application thereof, particularly in conventional aircraft. One of the reasons for this is believed to be the large errors generated in the sensor's outputs when it is subjected to ambient vibrations along or having substantial components along the disk spin axis at frequencies corresponding to the natural resonant frequency of the flexible rotor.
Generally, and as disclosed in the cited patents, there are two pairs of transducers or pick-offs, one pair for each sensing axis, the pick-offs of each pair being diametrically fixed to the housing adjacent the periphery of the disk and each pair being electrically connected in push-pull fashion. Thus, when the disk deflects or precesses due to an angular rate of the housing, one side of the disk deflects toward one of the pick-offs of the pair and away from the other, the outputs of both pick-offs differentially adding to produce an output signal proportional to the direction and magnitude of the input angular rate.
When the gyro is subjected to vibrations along the gyro spin axis at or near the resonant frequency of the flexible rotor, it has been found that unacceptably large steady state errors in the electrical signal outputs of the gyro occur. These errors are due to two phenomenon: (a) large axial displacements of the rotor periphery (in the same direction) due to such resonance, and (b) non-uniformity between the electrical output vs. deflection characteristics of the pick-offs of each pair. If, indeed the pick-offs had identical characteristics, their outputs due to axial displacements if the rotor periphery in the same direction would cancel. However, achieving such identity is difficult and of course costly.
The errors discussed above can be substantially reduced by concentrating on their primary cause, vis.: by reducing the axial displacement of the rotor periphery due to axial vibrations to as small a value as practical and hence reduce the effects of pick-off dissimilarity.